loadJS("js/gamekit/sylvester.js");
loadJS("js/gamekit/glUtils.js");

  var gl;
  function initGL(canvas) {
    try {
      gl = canvas.getContext("experimental-webgl");
      gl.viewportWidth = canvas.width;
      gl.viewportHeight = canvas.height;
    } catch(e) {
    }
    if (!gl) {
      alert("Could not initialise WebGL, sorry :-(");
    }
  }


  function getShader(gl, id) {
    var shaderScript = document.getElementById(id);
    if (!shaderScript) {
      return null;
    }

    var str = "";
    var k = shaderScript.firstChild;
    while (k) {
      if (k.nodeType == 3) {
        str += k.textContent;
      }
      k = k.nextSibling;
    }

    var shader;
    if (shaderScript.type == "x-shader/x-fragment") {
      shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (shaderScript.type == "x-shader/x-vertex") {
      shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
      return null;
    }

    gl.shaderSource(shader, str);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      alert(gl.getShaderInfoLog(shader));
      return null;
    }

    return shader;
  }


  var shaderProgram;
  function initShaders() {
    var fragmentShader = getShader(gl, "shader-fs");
    var vertexShader = getShader(gl, "shader-vs");

    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);

    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
      alert("Could not initialise shaders");
    }

    gl.useProgram(shaderProgram);

    shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);

    shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
    shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
  }


  var mvMatrix;

  function loadIdentity() {
    mvMatrix = Matrix.I(4);
  }


  function multMatrix(m) {
    mvMatrix = mvMatrix.x(m);
  }


  function mvTranslate(v) {
    var m = Matrix.Translation($V([v[0], v[1], v[2]])).ensure4x4();
    multMatrix(m);
  }


  var pMatrix;
  function perspective(fovy, aspect, znear, zfar) {
    pMatrix = makePerspective(fovy, aspect, znear, zfar);
  }


  function setMatrixUniforms() {
    gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, new Float32Array(pMatrix.flatten()));
    gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, new Float32Array(mvMatrix.flatten()));
  }



  var triangleVertexPositionBuffer;
  var squareVertexPositionBuffer;
  function initBuffers() {
    triangleVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
    var vertices = [
         0.0,  1.0,  0.0,
        -1.0, -1.0,  0.0,
         1.0, -1.0,  0.0
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    triangleVertexPositionBuffer.itemSize = 3;
    triangleVertexPositionBuffer.numItems = 3;

    squareVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
    vertices = [
         1.0,  1.0,  0.0,
        -1.0,  1.0,  0.0,
         1.0, -1.0,  0.0,
        -1.0, -1.0,  0.0
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    squareVertexPositionBuffer.itemSize = 3;
    squareVertexPositionBuffer.numItems = 4;
  }


  function drawScene() {
    gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);
    loadIdentity();

    mvTranslate([-1.5, 0.0, -7.0]);

    gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, triangleVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLES, 0, triangleVertexPositionBuffer.numItems);


    mvTranslate([3.0, 0.0, 0.0]);
    gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, squareVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems);
  }



function gameInit(glTarget) {

    stage = document.getElementById('mainStage');

    stage.src = "Loading WebGL.....";

    var targetCanvas = document.createElement('canvas');
    targetCanvas.width = 500;
    targetCanvas.height = 500;
    stage.appendChild(targetCanvas);

    initGL(targetCanvas);
    initShaders();
    initBuffers();

    gl.clearColor(0.0, 0.0, 0.0, 1.0);

    gl.clearDepth(1.0);

    gl.enable(gl.DEPTH_TEST);
    gl.depthFunc(gl.LEQUAL);

    setInterval(drawScene, 15);
  }

